What are the typical ECG (electrocardiogram) changes after the acute phase in patients who have had a STEMI (ST-Elevation Myocardial Infarction)?

Typical ECG Changes After the Acute Phase of STEMI

After the acute phase of STEMI, the most characteristic ECG changes include the development of pathological Q waves, resolution of ST-segment elevation, and the development of T-wave inversions in the affected leads. 1, 2

Evolution of ECG Changes Post-STEMI

Q Wave Development

• Pathological Q waves typically develop within hours to days after a STEMI and often persist indefinitely
• Defined as Q waves ≥0.03 seconds in duration and ≥0.1 mV deep, or QS complexes in leads I, II, aVL, aVF or V1-V6 in at least two contiguous leads 1
• In leads V2-V3, Q waves ≥0.02 seconds or QS complexes are considered pathological 1
• Q waves represent myocardial necrosis and are associated with higher 30-day mortality compared to patients without Q waves 3

ST-Segment Evolution

• ST-segment elevation typically resolves gradually over hours to days after successful reperfusion
• Complete resolution of ST-segment elevation is associated with better outcomes and more successful reperfusion
• Persistent ST-segment elevation may indicate unsuccessful reperfusion or ventricular aneurysm formation
• ST-segment depression in other leads often resolves as well

T-Wave Changes

• T-wave inversion typically develops after ST-segment resolution
• Persistent T-wave inversion (PTI) is independently associated with more extensive myocardial damage as visualized by cardiac magnetic resonance imaging 4
• The combination of Q waves and T-wave inversion on ECG indicates a more advanced stage of infarction and is associated with higher mortality 5
• T-wave inversions may persist for weeks, months, or indefinitely

Prognostic Significance of Post-STEMI ECG Changes

Q Waves

• Presence of Q waves indicates completed infarction with myocardial necrosis
• Associated with larger infarct size and worse left ventricular function
• Independent predictor of higher 30-day mortality (adjusted OR 1.44,95% CI 1.25-1.65) 3

T-Wave Inversions

• Persistent T-wave inversion correlates with larger infarct size on cardiac MRI (14[8-19]% vs. 3[1-8]% in patients without T-wave inversion) 4
• Patients with both Q waves and T-wave inversions have the highest 30-day and one-year mortality 5
• The amplitude of T-wave inversion is a better predictor of large chronic infarct size than Q-wave amplitude (AUC: 0.84 vs. 0.72) 4

Combined ECG Patterns

• Four distinct patterns with different prognostic implications 5:
  1. Q waves + T-wave inversion: Highest mortality
  2. Q waves without T-wave inversion: Higher early mortality
  3. T-wave inversion without Q waves: Higher late mortality
  4. Neither Q waves nor T-wave inversion: Lowest mortality

Clinical Implications

• ECG changes after the acute phase of STEMI provide valuable information about:

  • Extent of myocardial damage
  • Success of reperfusion therapy
  • Risk stratification for future events
  • Need for additional interventions

• Serial ECGs should be performed to monitor the evolution of these changes, particularly in the first days after STEMI

• The absence of Q wave development after STEMI may indicate successful early reperfusion with myocardial salvage

• Persistent ST-segment elevation beyond the acute phase may indicate ventricular aneurysm formation or unsuccessful reperfusion

Common Pitfalls in Interpretation

• Mistaking normal septal Q waves for pathological Q waves
• Failing to recognize persistent ST elevation as a sign of ventricular aneurysm
• Not accounting for pre-existing ECG abnormalities (prior infarction, left ventricular hypertrophy, bundle branch blocks)
• Overlooking the prognostic significance of persistent T-wave inversions

The combination of Q waves and T-wave inversions provides the most accurate assessment of infarct size and prognosis, with a Q-wave/T-wave score offering better risk stratification than either finding alone 4, 5.